Vehicle air conditioning systems include a compressor that compresses and superheats refrigerant, which then runs through a condenser, an expander and evaporator in turn before returning to the compressor to begin the cycle again. Mixed in with the refrigerant is a small amount of lubricating oil, which is entrained within the refrigerant and is needed to ensure the smooth performance of the compressor and to prolong the life of the compressor. Compressor life is directly related to the correct amount of oil reaching the compressor.
Interposed between the evaporator and compressor is an accumulator-dehydrator which is designed to accomplish several objectives. The accumulator-dehydrator primarily receives and accumulates the evaporator output. The evaporator output typically includes both a liquid component and a vapor component. The accumulator-dehydrator serves as a separator in which fluid collects at the bottom of the reservoir and vapor at the top. The accumulator-dehydrator ensures that only refrigerant in a vapor stage and entrained oil passes to the compressor. The accumulator-dehydrator prevents a liquid slug of refrigerant from being pulled or sucked into the compressor. Still further, a desiccant is typically located in the bottom of the accumulator-dehydrator to absorb any water in the refrigerant.
Traditionally accumulator-dehydrators are known to use a U-Shaped or J-Shaped tube more commonly known as a J-tube to direct vaporized refrigerant and draw in oil. The accumulator-dehydrator includes a canister with an inlet connected to the evaporator. The refrigerant enters the inlet as a vapor and liquid mixture. The liquid drops to the bottom of the canister and the vapor rises to the top. The J-tube is connected at one end to the canister outlet, which in turn is connected to the compressor. The J-tube extends down from the outlet to near the bottom of the canister and then turns upward and extends to near the top of the canister. The free end of J-tube, the portion near the canister top, is open to allow the vapor to be drawn into the J-tube and exit to the inlet of the compressor. A small opening is provided in the bottom turn-portion or U-portion of the J-tube to allow the liquid including the oil, to enter the J-tube and be entrained and delivered with the vapor to the compressor.
Traditionally, the rear system air conditioning lines were routed down stream of the accumulator-dehydrator into the compressor suction line. This design has the potential to send the rear air conditioning system liquid refrigerant directly to the compressor. If liquid refrigerant did reach the compressor it could cause failure. Because of this potential refrigerant "slugging", the rear air conditioning lines were routed into the accumulator-dehydrator to take advantage of the accumulator-dehydrator liquid separation capability. By changing the routing of the rear lines; however, a problem of oil accumulation in the rear air conditioning line developed when the front air conditioning system was on and the rear air conditioning system was off. The pressure and flow from the front line caused the oil in the accumulator-dehydrator to foam or splash and enter the rear lines and become trapped in the rear line. This collection of oil in the air conditioning line caused the percentage of oil available to the compressor to decrease. This had a negative effect on compressor durability. Sometimes this was corrected by placing an extra upward bend in the line approaching the accumulator-dehydrator. However, because of underhood space constraints and routing constraints this was difficult to package in most vehicles.